There are many ways to validate a value document, from simple to complex. Some methods involve visible (i.e. overt) features on or incorporated into a document, such as a hologram on a credit card, an embossed image or watermark on a bank note, a security foil, a security ribbon, colored threads or colored fibers within a bank note, or a floating and/or sinking image on a passport. While these features are easy to detect with the eye and may not require equipment for authentication, these overt features are easily identified by a would-be forger and/or counterfeiter. As such, in addition to overt features, hidden (i.e. covert) features may be incorporated in value documents. Covert features include invisible fluorescent fibers, chemically sensitive stains, fluorescent pigments or dyes that are incorporated into the substrate of the value document. Covert features may also be included in the ink that is printed onto the substrate of the value document or within the resin used to make films that are used in laminated value documents. Since covert features are not detectable by the human eye, detectors configured to detect these covert features are needed to authenticate the value document.
There are many validation systems (e.g. covert features and corresponding detectors) that are used to, for instance, authenticate bank notes. For example, U.S. Pat. No. 4,446,204 to Kaule, et al. discloses a security paper with authenticable features in the form of added or applied coloring agents which on the one hand make it possible to check the IR-transmission properties of the security paper, if appropriate, even in the printed image, and on the other hand have magnetic properties, wherein both IR Transmission and magnetic tests can be uninfluenced by one another but are capable of being carried out at the same position on the security paper. Known detection devices are then used to match detectors to the differently lying spectral region of the authenticable features for validation.
Further, U.S. Pat. No. 5,679,959 to Nagase discloses a bill discriminating apparatus that includes a light source for projecting a stimulating light onto a surface of a bill, a photomultiplier that photoelectrically detects the light emitted from the bill surface in response to the irradiation with the stimulating light and producing detected data corresponding to an amount of the detected light, a ROM for storing reference data, and a central processing unit (“CPU”) for comparing the detected data produced by the photomultiplier and the reference data stored in the ROM. Such a system, however, fails to detect a counterfeit document when the detected emitted radiation from the counterfeit is similar to the authentic emitted radiation parameter.
Many known validation systems involve detecting a covert authenticatable feature and evaluating its emission spectra. If the emissions alone are detected, then the value document is deemed authentic, otherwise it is rejected as a counterfeit. One problem with this type of existing validation system arises when the authenticatable feature is entirely contained in the printed ink on a substrate because it is subjected to wear and attrition loss. As a result, there is unpredictable deterioration of the authenticatable feature's emission spectra amplitude, and thus, the authentication apparatus may incorrectly identify an authentic document as a counterfeit. Another problem involves that fact that over time, this method has become less secure since counterfeiters have become more sophisticated and have greater access to scientific apparatus that can detect the incorporation of these features in value documents.
There are existing validation systems that involve detecting the decay time of a phosphor that is excited by a visible or ultraviolet light source in a stationary situation. For example, U.S. Pat. No. 7,030,371 to Vasic et al. discloses security documents or articles carrying luminescent marker compounds which show a time-deferred emission characteristic which are authenticated by a method and device that allows for rapid extraction of characteristic luminescent parameters, such as emission intensity and time constants. In addition, U.S. Publication No. 20090152468 to Allen et al. discloses a technique and apparatus for detecting infrared radiation emitted from a taggant material sample following the excitation of the sample by accurately measuring the decay time of the radiation of the particular taggant being used. These systems, however, do not involve detection and authentication of moving value documents.
U.S. Pat. No. 5,459,323 to Morgan discloses an apparatus for producing decay time weighted information (e.g. a decay time weighted image) of a luminescent sample, comprises an excitation light source arranged to illuminate the sample, means for modulating or pulsing the intensity of the excitation light in a predetermined cyclical manner, detector means for detecting photons emitted by the sample as a result of luminescence, means for storing data representative of detected photons, the stored data being weighted as a function of phase difference between detection of photons and the cyclically varying modulation, and means for producing decay time weighted information from the stored data. This technique, however, only works when the luminescent sample is stationary, since any movement of the sample compounds the phase difference detection.
Notwithstanding the existing validation systems for authenticating value documents, there exists a need for a system that reliably and accurately detects moving value documents, such as systems involved with sorting or detecting bank notes. The validation system should incorporate security features in and/or on the value document that are difficult to replicate and should have detection discrimination methods and features that are unique and complicated enough to prevent counterfeiting and forging of the value document. It is also important that these value documents such as bank notes can be authenticated at high speeds.